Retrievable stimulation frac plug with ball and seat

ABSTRACT

A retrievable stimulation frac plug for a well casing, having an elongate mandrel having a fluid bore, a valve seat, adapted to receive a sealing member for selectively sealing the fluid bore, a sealing mechanism for releasably sealing between the mandrel and the casing, a slip mechanism for releasably engaging the well casing, and a valve seat bypass, moveable between a closed position and an open position, adapted to provide a bypass past the valve seat.

FIELD

The present disclosure relates generally to hydrocarbon well workover tools. More particularly, the present disclosure relates to zonal isolation tools for use during well workovers and methods of using the zonal isolation tools.

BACKGROUND

In cased well completion or stimulation operations, it is sometimes desirable to isolate one section or zone of the well from another. This is commonly accomplished with a “bridge plug”.

It is known that certain, “drillable” bridge plugs may be drilled out to remove them from the well.

It is known that certain bridge plugs may be selectively activated, for example by a drop ball introduced into the well from surface, or other plugging systems.

It is known that certain bridge plugs may be retrievable, for example by retrieval from the well bore once the stimulation operation is complete.

One problem with conventional retrievable bridge plugs is that debris or other materials, for example frac sand or proppant, may accumulate on the top of the plug, which may make it difficult or even impossible to latch onto the plug for retrieval. The debris or other materials, may also accumulate in the annular region between the bridge plug and the casing, and may interfere with the release of the slips or the seals or both, making retrieval of the bridge plug more difficult or even impossible.

Another problem with conventional retrievable bridge plugs, in a multiple zone wellbore, where multiple retrievable bridge plugs are set to isolate the respective zones, is that it may be time and labour intensive to retrieve the multiple bridge plugs, one at a time, from the wellbore.

It is, therefore, desirable to provide an improved retrievable stimulation frac plug.

SUMMARY

It is an object of the present disclosure to obviate or mitigate at least one disadvantage of previous retrievable bridge plugs.

A retrievable stimulation frac plug for a well casing includes a mandrel having a fluid flow bore, a seal for sealing between the mandrel and the casing, and an anchor for anchoring the frac plug in the casing. A valve seat is adapted to receive a sealing member to selectively seal the fluid flow bore. A valve seat bypass is provided to selectively bypass the valve seat in order to allow circulation of fluid through the fluid flow bore, when the bypass is activated. Circulation through the fluid flow bore allows washing of the region below the retrievable stimulation frac plug and helps when retrieving multiple retrievable stimulation frac plugs in a single run.

In a first aspect, the present disclosure provides a retrievable stimulation frac plug for a well casing, including an elongate mandrel having a fluid bore, a valve seat adapted to receive a sealing member for selectively sealing the fluid bore, a sealing mechanism for releasably sealing between the mandrel and the well casing, a slip mechanism for releasably engaging the well casing, and a valve seat bypass, moveable between a closed position and an open position, adapted to selectively provide a bypass past the valve seat.

In an embodiment disclosed, the valve seat bypass includes a bypass sleeve extending along the mandrel, the mandrel having bypass port, and the bypass port sealed when the bypass sleeve is in a closed position and the bypass port open when the bypass sleeve is in an open position. In an embodiment disclosed, a shear pin retains the bypass sleeve in the closed position. In an embodiment disclosed, the bypass sleeve extends around the outside of the mandrel. In an embodiment disclosed, the valve seat is a ball seat. In an embodiment disclosed, the sealing member is a ball.

In an embodiment disclosed, the retrievable stimulation frac plug further includes a lower retrieval tool, the lower retrieval tool proximate a downhole end of the retrievable stimulation frac plug, wherein the lower retrieval tool is adapted to engage a lower stage retrievable stimulation frac plug.

In an embodiment disclosed, the lower retrieval tool includes a retrieval sleeve adapted to fit over the valve seat of the lower stage retrievable stimulation frac plug, providing a lower circulation passage between the lower retrieval tool and the lower stage retrievable stimulation frac plug, a bypass actuator adapted to move a lower stage bypass sleeve into an open position to open a lower stage bypass port through a lower stage mandrel of the lower stage retrievable stimulation frac plug, and a lower connector, adapted to engage an upper connector of the lower stage retrievable stimulation frac plug.

In a further aspect, the present disclosure provides a method of conducting a well operation in a well casing, including providing a retrievable stimulation frac plug having an elongate mandrel having a fluid bore, a valve seat, adapted to receive a sealing member for selectively sealing the fluid bore, a sealing mechanism for releasably sealing between the mandrel and the well casing, a slip mechanism for releasably engaging the well casing, and a valve seat bypass, moveable between a closed position and an open position, adapted to selectively provide a bypass past the valve seat, locating and setting the retrievable stimulation frac plug in the well casing, sealing the fluid bore, and conducting a well operation in the well casing above the retrievable stimulation frac plug.

In an embodiment disclosed, a ball is provided into the valve seat to seal the fluid bore. In an embodiment disclosed, the well operation includes perforating the well casing or frac-stimulation of a formation adjacent the well casing or both. In an embodiment disclosed, the methods are repeated for an additional number (n−1) of stages for a total number (n) stages.

In an embodiment disclosed, the method further includes providing a retrieval tool having a lower connector adapted to engage the stage n retrievable stimulation frac plug and actuate the valve bypass, deploying the retrieval tool to engage the stage n retrievable stimulation frac plug actuate the valve bypass, releasing the sealing mechanism and the slip mechanism of the stage n retrievable stimulation frac plug, moving the retrieval tool and the stage n retrievable stimulation frac plug down the well casing towards a stage n−1 retrievable stimulation frac plug, such that the lower retrieval tool of the stage n retrievable stimulation frac plug engages the stage n−1 retrievable stimulation frac plug.

In an embodiment disclosed, the method further includes circulating fluid through the circulation passage and through the fluid bore of the stage n retrievable stimulation frac plug prior to and/or while engaging the stage n−1 retrievable stimulation frac plug.

In an embodiment disclosed, the method further includes retrieving at least the stage n retrievable stimulation frac plug and the stage n−1 retrievable stimulation frac plug out of the well casing in a single run. In an embodiment disclosed, at least five retrievable stimulation frac plugs are retrieved in a single run. In an embodiment disclosed, substantially n retrievable stimulation frac plugs are retrieved in a single run.

Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

FIG. 1 is a frac plug of the present disclosure, in a well casing, with a setting tool;

FIG. 2 is a frac plug of the present disclosure, set in a well casing, with perforations above the retrievable stimulation frac plug;

FIG. 3 is a frac plug of the present disclosure, with a ball landed on a valve seat;

FIG. 4 depicts a plurality of frac plugs of the present disclosure in a multi-stage configuration;

FIG. 5 is a frac plug of the present disclosure, with an upper retrieval tool;

FIG. 6 is a frac plug of the present disclosure, with the upper retrieval tool set down to open a valve seat bypass to allow circulation through the frac plug;

FIG. 7 is a frac plug of the present disclosure, with the upper retrieval tool pulling tension upward to release the frac plug;

FIG. 8 is a frac plug of the present disclosure, depicting the upper retrieval tool and frac plug lowered downhole to a lower frac plug; and

FIG. 9 is the well casing, with all frac plugs withdrawn, leaving the well casing with an unrestricted open full bore.

DETAILED DESCRIPTION

Generally, the present disclosure provides a method and system for temporarily isolating one section of a well casing from another section of the well casing using a retrievable stimulation frac plug, for example to facilitate fracturing or otherwise stimulating the one section.

Referring to FIG. 1, a retrievable stimulation frac plug 10 is described for use with a well casing 20. The frac plug 10 includes a mandrel 30 having a fluid bore 40, a slip portion 50 comprising at least one slip mechanism 60 for releasably locking the frac plug 10 axially in the well casing 20, a seal portion 70 comprising at least one sealing mechanism 80 for releasably sealing between the mandrel 30 and the well casing 20, and a valve seat 90 for receiving a sealing member, for example a ball 100 (see FIG. 3) for selectively sealing the fluid bore 40. In an embodiment disclosed, the mandrel 30 (and the fluid bore 40) is split into a lower section and an upper section, threaded together (as shown) to facilitate assembly of the frac plug 10.

A valve seat bypass 110, moveable between a closed position 120 and an open position 130 (see FIG. 7), provides a bypass past the valve seat 90. The valve seat bypass 110 includes a bypass sleeve 140 extending along the mandrel 30. The mandrel 30 includes at least one bypass port 150, which is sealed when the bypass sleeve 140 is in the closed position 120, and which is open when the bypass sleeve 140 is in the open position 130. The bypass sleeve 140 is held in the closed position 120 by shear screw 160, and is moved into the open position by application of an axial force, for example by an upper retrieval tool 170 (see FIG. 5) or a lower retrieval tool 180, as the case may be. When the bypass sleeve 140 is in the open position 130 (see FIG. 7), fluid may be circulated past the valve seat 90 through the bypass port 150 and through the mandrel 30 via the fluid bore 40 to provide pressure equalization across the frac plug 10 or fluid circulation through the frac plug 10 or both.

The slip mechanism 60 includes annular slips 190 mounted within a slip cage 200 having slip springs 210 biasing the slips 190 inward, toward the mandrel 30. The slips 190 are mounted between an upper cone 220 and a lower cone 230. The lower cone 230 is fixed to the mandrel 30. An O-ring 240 seals between the lower cone 230 and the mandrel 30.

The sealing mechanism 80 includes one or more annular sealing elements 250 mounted between an upper gauge ring 260 and a lower gauge ring 270 on a setting sleeve 280. In an embodiment, the setting sleeve 280 is moveable relative to the mandrel 30. In an embodiment disclosed, the sealing mechanism 80 includes a plurality of sealing elements 250. In an embodiment disclosed, a spacer 290 sits between adjacent sealing elements 250. An O-ring 300 seals between the mandrel 30 and the upper gauge ring 260.

A lower shear sub 310 connects the upper cone 220 of the slip mechanism 60 and the setting sleeve 280. A shear screw 320 pins the connection between the lower shear sub 310 and the setting sleeve 280. In an embodiment disclosed, the frac plug 10 is set by providing relative force upward on the mandrel 30 or downward on the setting sleeve 280 or both to activate the slip mechanism 60 and the sealing mechanism 80.

An upper connector 330 (see FIG. 2) is connected with the upper gauge ring 260 through a release shear sub 340 and an upper shear sub 350. The connection between the upper connector 330 and the upper shear sub 350 includes an upper ratchet 360. The connection between the upper shear sub 350 and the release shear sub 340 includes a release shear sleeve 370. A shear screw 380 pins the connection between the upper shear sub 350 and the mandrel 30. A shear screw 390 pins the connection between the release shear sub 340 and the release shear sleeve 370.

In an embodiment disclosed, a wiper or deflector 400 proximate the connector 330 provides an annular seal between the frac plug 10 and the well casing 20, such that materials, such as sand or other proppant from stimulation operations, or other materials do not collect on top of or around the workings of the frac plug 10.

The frac plug 10 includes or is adapted to connect with a lower retrieval tool 180. The lower retrieval tool 180 includes a lower connector 410 adapted to mate with and engage an upper connector 330 and a bypass actuator 420 to actuate the bypass sleeve 140 of another frac plug 10. This provides the ability of the frac plug 10 with the lower retrieval tool 180 to be moved downhole and retrieve another frac plug 10 (for example in a multi-stage frac for a multi-stage retrieval).

Setting

The frac plug 10 may be set or released using apparatus and methods known to one skilled in the art. In an embodiment disclosed, a setting tool 430 includes a sleeve adaptor 440 for connecting the setting tool 430 and a work string 450, such as coiled tubing. A setting sleeve 460 extends downward from the sleeve adapter 440 and terminates with a setting sleeve end cap 470. The setting sleeve end cap 470 is adapted to mate with, but not latch onto the upper connector 330 of the retrievable stimulation frac plug 10, for example by abutting a connector face 480. The setting tool 430 may be used to apply a downward force upon the frac plug 10. The frac plug 10 with the setting tool 430 may be located in the well casing 20 via the work string 450 or preferably may simply be pumped down the well casing 20 by fluid pressure.

The setting tool 430 includes a shear rod 490 which engages the valve seat 90 prior to setting the frac plug 10. The shear rod 490 is releasably held in place with a shear screw 500. A connecting stud 510 is used to connect the shear rod 490 and an adapter 520, and a setting string 530, such as a wireline or a slickline connects to the adapter 520.

The setting tool 430 may be used to place the retrievable stimulation frac plug 10 at a desired location in the well casing 20. The retrievable stimulation frac plug 10 may then be set by providing a relative upward pull on the shear rod 490 while holding the setting sleeve 460 in place—for example by applying a downward holding force to work string 450 while applying an upward pulling force on the setting string 530. As force is applied to shear rod 490, the slip mechanism 60 is activated, the shear screws 320 and 380 are sheared, and the sealing mechanism 80 is activated, and upon the application of a greater sufficient force, the shear screw 500 will shear, releasing the shear rod 490 from the valve seat 90, and the retrievable stimulation frac plug 10 will be set in place (see FIG. 2). The upper ratchet 360 holds the frac plug 10 in the set position.

Perforating and Fracturing

Referring to FIGS. 2 and 3, with the frac plug 10 set, perforations 535 may be provided through the well casing 20 to establish communication between the well casing 20 and a subterranean formation 540.

Referring to FIG. 3, the fluid flow bore 40 is sealed by providing a sealing member, such as a ball 100 into the well casing 20. The ball 100 lands in the valve seat 90 and seals the fluid flow bore 40. The annular sealing elements 250 seal between the mandrel 30 and the well casing 20 and the ball 100 seals the fluid flow bore 40. The well casing 20 above the frac plug 10 is thus isolated from the well casing 20 below the frac plug 10.

A well operation may be performed above the frac plug 10, isolated from the well casing 20 below the frac plug 10. The well operation may include one or more completion or stimulation procedures known to a person skilled in the art, for example, perforating, fracturing, chemical treatment, or combinations thereof. In an embodiment, the well operation includes fracturing.

Multi-Stage

The steps above may be repeated one or more times to provide a multi-stage completion or stimulation procedure. Referring to FIG. 4, the placement and setting of a frac plug 10, providing the perforations 535 through the well casing 20, and stimulation of a section of the subterranean formation 540, together forming a “stage” is repeated one or more times in sequence to provide a multi-stage operation along the well casing 20, with each subsequent stage being in an uphole direction from the previous stage.

It is not uncommon for such multi-stage operations to include 20 or even 40 stages, but for example only, a two-stage operation is shown for simplicity.

A first-stage 800.1 includes the steps described above in relation to the frac plug 10.1, that is position the frac plug 10.1, set it in place activating the slip mechanism and seal mechanism, provide ball 100.1 to seal the bore 40.1 and providing the perforations 535.1 through the well casing 20, and stimulation of a section of the subterranean formation 540.1. A second-stage 800.2 is then provided above (uphole relative) the first-stage 800.1. The second-stage 800.2 includes the steps described above in relation to the frac plug 10.2. That is position the frac plug 10.2, set it in place activating the slip mechanism and seal mechanism, provide ball 100.2 to seal the bore 40.2 and providing the perforations 535.2 through the well casing 20, and stimulation of a section of the subterranean formation 540.2.

The setting steps may be repeated for multiple stages, 800.1, 800.2, etc. to 800.n utilizing frac plugs 10.1, 10.2, etc. to 10.n, where n is the number of stages.

Retrieval and Circulation

Referring to FIG. 5, an upper retrieval tool 170 includes a lower connector 550 adapted to mate with and engage the upper connector 330 of the frac plug 10. The retrieval tool 170 also provides a bypass actuator 560 which engages the bypass sleeve 140 to operate the valve seat bypass 110. Fluid may be circulated through the work string 450 to flush ahead of the retrieval tool 170 and wash any sand or debris from the upper connector 250.

Referring to FIGS. 6 and 7, as force is applied by the bypass actuator 560 to the bypass sleeve 140, the shear screw 160 is sheared, and the bypass sleeve 140 moves from the closed position 120 to the open position 130 (FIG. 7). The lower connector 550 mates with and engages the upper connector 330 of the frac plug 10.

With the valve seat bypass 110 in the open position 130 (FIG. 7), a flow passage 570 extends around (bypassing) the valve seat 90 and ball 100 and through the at least one bypass port 150, and thus fluid may be circulated through the frac plug 10. This can be used to equalize pressure or to facilitate circulation or washing ahead of the retrieval tool 170, for example to wash the upper connector 330 of a lower frac plug 10.

The lower connector 550 of the upper retrieval tool 170 mates with and engages the upper connector 330 of the frac plug 10, and the frac plug 10 is released by applying an upward force (pull) to the upper retrieval tool 170. The upward pull causes shear screw 390 to shear (effectively releasing the upper ratchet 360) allowing relative movement between the release shear sleeve 370 and the release shear sub 340 releasing the sealing mechanism 80 and the slip mechanism 60.

The frac plug 10 is then axially free within the well casing 20 and may be retrieved to surface. However, more commonly, the assembly (upper retrieval tool 170, frac plug 10, and lower retrieval tool 180) may instead be moved in a downhole direction to pick up one or more additional frac plugs 10, prior to retrieval to surface. Again, fluid may be circulated through the upper retrieval tool 170 and through the valve seat bypass 110 and the bypass port 150 to equalize pressure or to facilitate circulation or washing ahead of the assembly (through the fluid bore 40 and out the lower retrieval tool 180), for example to wash the upper connector 330 of a further frac plug 10.

Multi-Stage Retrieval

Referring to FIG. 8, the retrieval tool 170 has been used to release the frac plug 10.2 in a second-stage 800.2 (and open the bypass sleeve 140 and the bypass port 150), and this assembly has been moved downhole to engage the frac plug 10.1 in a first-stage 800.1. Again, fluid may be circulated through the upper retrieval tool 170 and through the valve seat bypass 110.2 and the bypass port 150.2 to equalize pressure or to facilitate circulation or washing ahead of the assembly (through the lower retrieval tool 180.2), for example to wash the upper connector 330.1 of the frac plug 10.1.

The lower retrieval tool 180 of the frac plug 10.2 (of second-stage 800.2) can then be used to release and retrieve the frac plug 10.1 (of first-stage 800.1). The entire assembly (upper release tool 170, frac plug 10.2, and frac plug 10.1) may then be retrieved to surface.

This example illustrates two stages for simplicity. It is much more typical to use n-stages, where n may be 20 or 40 or more. In such a case, the retrieval tool 170 would be used to release the frac plug 10.n (of the n-stage 800.n), and the assembly moved downhole. Fluid may be circulated through the frac plug 10.n to wash ahead of the assembly. The lower retrieval tool 180 would be used to engage and release the next frac plug 10.(n−1) (of the n−1)-stage 800.(n−1), and so on until a selected number of stages are retrieved to surface in a single run.

In an embodiment disclosed, where the plurality of frac plugs 10 to be retrieved becomes large, for example twenty (20) or more, they need not all be retrieved at the same time, and may instead be retrieved in convenient or practical groups, for example, groups of 5 or 10 may be retrieved in a single run, as the case may be. In an embodiment disclosed, the frac plugs 10 are retrieved in groups of more than 5 stages in a single trip.

Full Bore Opening

Referring to FIG. 9, when all of the frac plugs 10 have been removed from the well casing 20, what remains is the well casing 20 which has perforations 535 and the subterranean formation 540 stimulated in multiple stages. Here eight (8) stages (800.8, 800.7, 800.6, 800.5, 800.4, 800.3, 800.2, and 800.1) are shown for example only, having perforations 535.8, 535.7, 535.6, 535.5, 535.4, 535.3, 535.2, 535.1, and the adjacent subterranean formation 540.8, 540.7, 540.6, 540.5, 540.4, 540.3, 540.2, 540.1. However, more commonly, the number of stages may approach twenty (20) or forty (40) or more.

In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required. In other instances, well-known structures and components are shown in block diagram or simplified form in order not to obscure the understanding.

The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto. 

What is claimed is:
 1. A retrievable stimulation frac plug for a well casing, comprising: an elongate mandrel having a fluid bore; a valve seat, adapted to receive a sealing member for selectively sealing the fluid bore; a sealing mechanism for releasably sealing between the mandrel and the well casing; a slip mechanism for releasably engaging the well casing; and a valve seat bypass, moveable between a closed position and an open position, adapted to selectively provide a bypass past the valve seat.
 2. The retrievable stimulation frac plug of claim 1, the valve seat bypass comprising a bypass sleeve extending along the mandrel, the mandrel having bypass port, and the bypass port sealed when the bypass sleeve is in a closed position, and the bypass port open when the bypass sleeve is in an open position.
 3. The retrievable stimulation frac plug of claim 2, further comprising a shear pin for retaining the bypass sleeve in the closed position.
 4. The retrievable stimulation frac plug of claim 2, wherein the bypass sleeve extends around the outside of the mandrel.
 5. The retrievable stimulation frac plug of claim 2, wherein the valve seat is a ball seat.
 6. The retrievable stimulation frac plug of claim 2, wherein the sealing member is a ball.
 7. The retrievable stimulation frac plug of claim 1, further comprising a lower retrieval tool, the lower retrieval tool proximate a downhole end of the retrievable stimulation frac plug, wherein the lower retrieval tool is adapted to engage a lower stage retrievable stimulation frac plug.
 8. The retrievable stimulation frac plug of claim 7, the lower retrieval tool comprising: a retrieval sleeve, adapted to fit over the valve seat of the lower stage retrievable stimulation frac plug, providing a lower circulation passage between the lower retrieval tool and the lower stage retrievable stimulation frac plug; a bypass actuator adapted to move a lower stage bypass sleeve into an open position to open a lower stage bypass port through a lower stage mandrel of the lower stage retrievable stimulation frac plug; and a lower connector, adapted to engage an upper connector of the lower stage retrievable stimulation frac plug.
 9. A method of conducting a well operation in a well casing, comprising: a. providing a retrievable stimulation frac plug having: an elongate mandrel having a fluid bore; a valve seat, adapted to receive a sealing member for selectively sealing the fluid bore; a sealing mechanism for releasably sealing between the mandrel and the well casing; a slip mechanism for releasably engaging the well casing; and a valve seat bypass, moveable between a closed position and an open position, adapted to selectively provide a bypass past the valve seat; b. locating and setting the retrievable stimulation frac plug in the well casing; c. sealing the fluid bore; and d. conducting a well operation in the well casing above the retrievable stimulation frac plug.
 10. The method of claim 9, the sealing the fluid bore comprising providing a ball into the valve seat to seal the fluid bore.
 11. The method of claim 9, the well operation comprising perforating the well casing or frac-stimulation of a formation adjacent the well casing or both.
 12. The method of claim 9, further comprising repeating (a), (b), (c), and (d) for an additional number (n−1) of stages for a total number (n) stages.
 13. The method of claim 12, further comprising: a. providing a retrieval tool having a lower connector adapted to engage the stage n retrievable stimulation frac plug and actuate the valve bypass; b. deploying the retrieval tool to engage the stage n retrievable stimulation frac plug actuate the valve bypass; c. releasing the sealing mechanism and the slip mechanism of the stage n retrievable stimulation frac plug; d. moving the retrieval tool and the stage n retrievable stimulation frac plug down the well casing towards a stage n−1 retrievable stimulation frac plug, such that the lower retrieval tool of the stage n retrievable stimulation frac plug engages the stage n−1 retrievable stimulation frac plug.
 14. The method of claim 13, further comprising circulating fluid through the circulation passage and through the fluid bore of the stage n retrievable stimulation frac plug prior to and/or while engaging the stage n−1 retrievable stimulation frac plug.
 15. The method of claim 13, further comprising retrieving at least the stage n retrievable stimulation frac plug and the stage n−1 retrievable stimulation frac plug out of the well casing in a single run.
 16. The method of claim 13, further comprising retrieving at least five retrievable stimulation frac plugs in a single run.
 17. The method of claim 13, further comprising retrieving substantially n retrievable stimulation frac plugs in a single run. 